The invention concerns a sensor device for registering voltage levels on corrosion exposed structures. These structures may be pipes and supports in offshore environments, to which a voltage is supplied so that an excitation current flows in the structure. The invention also concerns a method for performing measurements with such a sensor device. The device may be utilized for detection of internal and external corrosion, crack formation, erosion and other defects.
NO patent No. 150 136 teaches a method and a device for monitoring steel constructions in order to detect defects, e.g. cracks. By this system fixed measuring points are utilized to register voltage drops when an excitation current is supplied. By comparing the voltage drop at a certain site and a certain time with previously registered measurements at the same site, any development of defects to both sides of the measuring area can be detected.
However, in some cases, it is not convenient to perform measurements with such fixed measuring points, both due to the measuring points themselves, which need to be attached at several places, and due to their connections. The attachment of fixed measuring points may involve welding, which is undesirable in areas where there is a danger of explosion.
It is therefore a main objective of the present invention to provide a convenient sensor device for mobile or periodical (portable or semi portable) use at a measurement site, so that welded measurement points are not required.
It is a further objective to provide a sensor device which can be installed and used without safety risks in explosion hazard areas.
It is a particular objective to provide a sensor device with an elongated shape, a low production cost, a low height, and which can easily be assembled.
It is a still further objective to provide a measurement method which does not require a continuos connection of sensors as prescribed in NO 150 136, but which can rely on short time measurements. Singular measurements should permit calculation of wall thickness.
A pliable or jointed band configuration allows for easy adaption of this sensor device to various structures. One embodiment is especially convenient for pipes, while another embodiment is easily adapted for various other structures. Both are easy to set tip and remove.
These structures allow xe2x80x9csnapshotxe2x80x9d measurements. This gives the particular advantage that it does not require continuous operation, it may be performed in minutes with a free choice of intervals and without any need for measurement equipment and/or connections at the measurement site between each measurement. The intervals may be quite long, e.g. weeks or months.